The following background information is being provided to assist the reader in understanding the environment in which the invention will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document.
Examples of moving a load over a predetermined path which also varies in a vertical direction, hereinafter referred to as an attitude, include an apparatus for moving a work holding table for metal cutting equipment, a powered apparatus for moving a sliding door of a minivan, a conveyor for moving a load between changing attitude levels, a powered accessibility device for a transit vehicle, and powered door systems for transit vehicles.
In many instances changing attitude levels may affect proper movement of the load if such attitude is not compensated for prior to the load movement. This is particularly the case in a transit vehicle which operates over various terrain attitudes and conditions affecting door operation.
In a first aspect, a vehicle may be stopped on a terrain surface which is graded in a longitudinal direction, hereinafter referred to as a pitched attitude measured by a degree of pitch, affecting opening and closing of the doors that move parallel to the vehicle structure. In such condition, when the door opening movement is toward the rear of the vehicle, the door will tend to open faster and close slower due to its own weight. When the door opening movement is toward the front of the vehicle, the door will tend to open slower and close faster due to its own weight.
In a second aspect, the vehicle may be stopped on a terrain surface which is graded in a lateral direction, hereinafter referred to as a rolled attitude measured by a degree of roll, affecting opening and closing of the doors that move perpendicular to the vehicle structure. In such condition, when the vehicle is rolled toward its side used for passenger ingress and egress, the door will tend to open faster and close slower due to its own weight. On the other hand, when the vehicle is rolled away from its side used for passenger ingress and egress, the door will tend to open slower and close faster due to its own weight.
As would normally be expected, a much more severe condition for movement of the door is encountered when the transit vehicle is stopped on the terrain surface which combines both roll and pitch attitudes.
In a third aspect, if a transit vehicle exhibits higher rolling levels due to lower tire pressure and/or wheel wear, a door of a larger size may obstructed against a stationary object such as a curb or platform.
It is generally well known in the transit vehicle art to employ a door member engageable with a powered door operator and driven thereby to cover and uncover an aperture of the transit vehicle. The door is either attached to a driving means of a stationeryly disposed hanger member to achieve a sliding motion or to a pivotally disposed member to achieve a swinging motion. The powered door operators are either of electric, pneumatic or hydraulic types.
To expedite passenger ingress and egress and minimize a dwell time of the transit vehicle at a stop, door opening and closing time intervals have been aggressively set in a 1 to 5 second range. Opening and closing door movements must be controlled in a manner providing smooth, continuous and accurate motion under all design and operating conditions and without bouncing at either end of the movement. Additionally, in a transit vehicle having a multiplicity of door systems, all doors must open and close, for all practical purposes, within an identical time interval. These requirements are especially challenging to meet with pneumatic type door systems due to inherent system response delays and pressure fluctuations of the air pressure supply.
Accordingly, it will be appreciated that a door control system must attain a certain level of precision in order to meet the aforementioned requirements. Newer pneumatic or hydraulic systems may employ electronically controlled variable valves capable of modulating fluid pressure in order to achieve desired door movement. However, older and less sophisticated hydraulic or pneumatic control systems employ on/off discrete pressure valve controls and thus lack the ability to respond to fluctuating operational parameters.
Newer microprocessor based control systems, especially for electric door operators, employ position feedback mechanisms and execute closed-loop motion control algorithms capable of varying a motion profile over the range of the motion. A commonly employed motion profile is based on the velocity control using a well known trapezoidal profile. Such trapezoidal profile changes velocity in a linear fashion until the target velocity is reached. The profile consists of acceleration phase, constant velocity phase and deceleration phase graphically representing a trapezoid. Closed-loop control systems compare measured output of the system with predetermined values and take corrective actions by varying velocity in order to achieve desired door movement. Such comparison and corrective actions are performed throughout a substantial portion of the door movement, generally after the completion of the acceleration phase.
Alternatively, a position control, a torque control or a current control method may be used for door movement.
U.S. Pat. No. 6,064,165 issued to Boisvert et al teaches a method and apparatus for controlling motion of a motor driven element in a vehicle over a range of motion wherein a sensor continuously measures a motor parameter and each subsequent measurement is compared with the previous one to determine its placement in a predetermined motion range. The values of the threshold parameter range vary with a position of the motor driven element over such range of motion or an elapsed time of movement. A controller coupled to the comparator alters the motion of the driven element if the measured parameter falls outside of the range.
A disadvantage of presently used motion control methods is that the door accelerates and decelerates during the range of the motion to achieve a predetermined motion control profile and complete such motion in a predetermined time interval. Even though door accelerations and decelerations may not be obvious to one observing door motion, they may decrease component durability by diminishing door movement with a constant speed value.
Such an approach further places additional constraints onto an obstruction detection algorithm executed by the control system as it now has to determine whether parameter fluctuations are due to obstruction or are due to other factors such as vehicle attitude described below.
The presently employed control systems lack a capability to recognize abovementioned surface attitudes prior to initiating door movement thus resulting in increased motion corrections during the range of the movement. This further affects the ability of the door to move within a predetermined time interval, especially at the lower end of the range, and additionally affects movement synchronicity of a plurality of doors on the vehicle.
Another long felt need related to door system operation is the ability to recognize shock and vibration levels prior to initiating door movement. Although this is the case in an opening direction, it is especially the case in a closing direction. Such shock and vibration levels increase the initial resistance to movement and further affect timing of the door movement.
As it can be seen from the above discussion, there is a need for door system attitude compensation prior to initiating door movement, especially for door systems that do not employ newer microprocessor controls.